Last night, or earlier today depending on your time zone, Apple pushed three silent updates: the two to Gatekeeper data and MRT were relatively routine, but the third, to “Compatibility Notification Data”, was a first as far as I can tell, and only for macOS Mojave. This brief article explains what I think that third update is.

If you’re running Mojave, you should now have a bundle at /System/Library/CoreServices/CompatibilityNotificationData.bundle: that’s what was installed. As far as I can tell, it didn’t exist there before in macOS 10.14.5. It’s active ingredient is a Property List, CompatibilityNotificationData.plist, stored in its Resources folder, and it contains no executable code but is signed.

Inside this Property List are dictionaries inside dictionaries, which list apps which aren’t 64-bit and therefore will be incompatible with Catalina. Each is given a minimum and maximum version number, and may be assigned to an app group. For example, the maximum version for Apple’s old app Aperture is given as 4.0 (its last release version was 3.6, so this includes all released copies of Aperture), and it’s assigned an Application Name rather than a group.

Microsoft Office components, both the main apps like Word and its many helper apps, are included. For example, the maximum version of Word given is 14.9, which compares with 14.7.7 in Microsoft Office 2011, and 16.26 in the current Office 365. Word is grouped with MicrosoftOffice2011GroupKey, as are all the other components of Office 2011.

This bundle is clearly part of preparations for migration to Catalina. The data might be used by the existing Legacy Software item in System Information, but might also be required for another tool which will ship with the 10.14.6 update, due very soon now.

You may find this list a useful reference. Ensure that you make a copy to view in a text or XML editor, rather than opening the original, if you intend doing that.

Currently, “Compatibility Notification Data” isn’t tracked by SilentKnight or LockRattler, but its installation is recorded by SystHist. As it isn’t related to security and will most probably prove of temporary importance, I don’t intend adding it to the already long list of data which those apps keep tabs on. If you want to check its version number, simply select the bundle and the Finder will reveal that for you.